Democratic presidential candidate Hillary Clinton speaks to guests at a campaign event Nov. 3 in Coralville, Iowa. Getty Images

Former Secretary of State Hillary Clinton is beating Vermont Sen. Bernie Sanders in more than just the polls for the 2016 Democratic primary. She's racked up more than 120 congressional endorsements -- 31 of which are in the Senate, where Sanders serves -- to his two. Sanders told CNN this week that should send voters a message.

"It tells you that one of us is a candidate of the establishment," Bloomberg reported Sanders said in a "New Day" interview that aired Monday. "One of us is involved in establishment politics and establishment economics, and it says that maybe the other candidate is prepared to take on the establishment."

Clinton was leading Sanders by about 25 percentage points Monday with the backing of 56.4 percent of likely Democratic primary voters, according to the HuffPost Pollster. Sanders told CNN he wasn't concerned -- over the past six months, he's left behind his "fringe candidate" reputation and become someone the media is telling "you haven't quite won this thing yet."

As of Sunday afternoon, the Hill reported Clinton had 127 congressional endorsements from Democrats, including New Jersey Sen. Cory Booker, Missouri Sen. Claire McCaskill and Illinois Sen. Dick Durbin. Sanders had the support of two Democratic members of the House: Minnesota Rep. Keith Ellison and Arizona Rep. Raúl Grijalva.

“It’s a stamp of approval, essentially, and a cue to voters that the candidate is acceptable,” Marty Cohen, an associate political science professor at James Madison University in Harrisburg, Virginia, told USA Today. “Also, we think of (endorsements) as a promise of resources, whether they be money, campaign volunteers and an opportunity for another elected official to put their apparatus to work for the candidate they endorse.”

On the Republican side, former Florida Gov. Jeb Bush -- who was polling in fifth place among GOP candidates Monday -- had the most congressional endorsements, with 17. Neither of the race's two front-runners, real estate tycoon Donald Trump and retired neurosurgeon Ben Carson, had any.